Aneuploidy in the embryonic progeny of females heterozygous for the Robertsonian chromosome (9.12) in genetically wild Peru-Coppock mice (Mus musculus).

The spontaneous appearance of a Robertsonian translocation in a laboratory colony of genetically wild Peru-Coppock mice gave the opportunity to study potential meiotic nondisjunction soon after the formation of the new chromosome and also in a hitherto untested combination of genotype and environment Metaphase II scores from the progenitor male had indicated a nondisjunction rate of approximately 10%, a figure that was confirmed by the finding of an estimated 12-16% total trisomic and probable monosomic zygotes in chromosomal studies of Day 9 embryos from heterozygous females. The chromosome studies also showed the presence of a significant excess of normal embryos that were heterozygous for the Robertsonian chromosome.